U.S. patent application number 09/898413 was filed with the patent office on 2001-11-15 for scanned beam display with adjustable accommodation.
Invention is credited to Johnston, Richard S., Kollin, Joel S., Melville, Charles D., Tidwell, Michael.
Application Number | 20010040535 09/898413 |
Document ID | / |
Family ID | 22695455 |
Filed Date | 2001-11-15 |
United States Patent
Application |
20010040535 |
Kind Code |
A1 |
Tidwell, Michael ; et
al. |
November 15, 2001 |
Scanned beam display with adjustable accommodation
Abstract
A scanning beam display controls the curvature of scanning light
wave impinging on the eye to simulate image points of differing
depth. To simulate an object at a far distance the generated light
waves are flatter. To simulate closer objects, the light wave
curvature increases. When changing the curvature of the light
waves, the eye responds by altering its focus. The curvature of the
light waves thus determines the apparent focal distance from the
eye to the virtual object. To vary the curvature, either a variable
focus lens or a variable index of refraction device is used.
Alternatively, a moving point source is used. The generated
apparent distance of a virtual object is correlated to a detected
distance in a background field of view. Intensity of the virtual
object is correlated to detected intensity of background light.
Inventors: |
Tidwell, Michael; (Seattle,
WA) ; Melville, Charles D.; (Issaquah, WA) ;
Johnston, Richard S.; (Issaquah, WA) ; Kollin, Joel
S.; (Long Island City, NY) |
Correspondence
Address: |
Steven P. Koda, Esq.
KODA LAW OFFICE
P.O. Box 10057
Bainbridge Island
WA
98110
US
|
Family ID: |
22695455 |
Appl. No.: |
09/898413 |
Filed: |
July 3, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09898413 |
Jul 3, 2001 |
|
|
|
09188993 |
Nov 9, 1998 |
|
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Current U.S.
Class: |
345/32 |
Current CPC
Class: |
G02B 2027/0178 20130101;
G02B 27/0172 20130101; G02B 27/0176 20130101; G02B 27/017 20130101;
G09G 3/025 20130101; G09G 3/003 20130101 |
Class at
Publication: |
345/32 |
International
Class: |
G09G 003/00 |
Claims
What is claimed is:
1. A scanning display apparatus, comprising: an image signal source
operative to produce an image signal; a focal control signal source
generating a focal control signal; a light emitter coupled to the
image signal source and responsive to the image signal to emit
light; a lens which receives light from the light emitter and which
passes exiting light, the exiting light having a focal distance;
and a controller responsive to the focal control signal for
controlling distance between the light emitter and the lens,
wherein the focal distance of the light exiting the lens varies
with the distance between the light emitter and the lens.
2. The apparatus of claim 1, in which the controller comprises an
electromagnetic drive circuit.
3. The apparatus of claim 1, in which the controller comprises a
piezoelectric actuator.
4. The apparatus of claim 1, in which the light emitter is one of a
plurality of light emitters coupled to the image signal source and
responsive to the image signal to emit light toward the lens.
5. The apparatus of claim 1, serving as an augmented display, and
further comprising a beamsplitter which receives the exiting light
and which further receives background light.
6. The apparatus of claim 1, further comprising a light sensor
which detects intensity of the background light and a controller
which responds to the detected intensity to control intensity of
the emitted light.
7. The apparatus of claim 1, further comprising a signal source
responsive to the received background light which varies the focal
control signal to correlate the controlled distance to the
background light.
8. The apparatus of claim 7, further comprising a distance sensor
which detects distance of an object within a background field of
view from which the background light is received, and wherein the
signal source is responsive to the received background light from
the object and varies the focal control signal to correlate the
controlled distance to the detected distance of the object.
9. A scanning display apparatus, comprising: an image signal source
operative to produce an image signal; a focal control signal source
generating a focal control signal; a light emitter coupled to the
image signal source and responsive to the image signal to emit
light; a mirror receiving the light from the light emitter, the
mirror movable about an axis in response to the focal control
signal to vary an angle at which the light is reflected from the
mirror; and a lens which receives light from the mirror and which
passes exiting light, the exiting light having a focal distance,
wherein the angle of the mirror determines the focal distance of
light exiting the lens.
10. The apparatus of claim 9, in which the light emitter is one of
a plurality of light emitters coupled to the image signal source
and responsive to the image signal to emit light toward the lens.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a divisional of U.S. patent application Ser. No.
09/188,993 filed Nov. 9, 1998 of Michael Tidwell et al. for
"Scanned Beam Display with Adjustable Acommodation." The content of
such application is incorporated herein by reference and made a
part hereof.
[0002] This invention is related to U.S. patent application Ser.
No. 09/009,759 filed Jan. 20, 1998 of Charles D. Melville for
Augmented Imaging Using A Silhouette To Improve Contrast. This
invention also is related to U.S. patent application Ser. No.
09/188,991 filed Nov. 9, 1998 of Charles D. Melville et al. for
Method and Apparatus for Scanning Optical Distance. The content of
all such applications are incorporated herein by reference and made
a part hereof.
BACKGROUND OF THE INVENTION
[0003] This invention relates to scanning beam display devices, and
more particularly to optical configurations for scanning beam
display devices.
[0004] A scanning beam display device is an optical device for
generating an image that can be perceived by a viewer's eye. Light
is emitted from a light source, collimated through a lens, then
passed through a scanning device. The scanning device defines a
scanning pattern for the light. The scanned light converges to
focus points of an intermediate image plane. As the scanning
occurs, the focus point moves along the image plane (e.g., in a
raster scanning pattern). The light then diverges beyond the plane.
An eyepiece is positioned along the light path beyond the
intermediate image plane at some desired focal length. An "exit
pupil" occurs shortly beyond the eyepiece in an area where a
viewer's eye is to be positioned.
[0005] A viewer looks into the eyepiece to view an image. The
eyepiece receives light that is being deflected along a raster
pattern. Light thus impinges on the viewer's eye pupil at differing
angles at different times during the scanning cycle. This range of
angles determines the size of the field of view perceived by the
viewer. Modulation of the light during the scanning cycle
determines the content of the image.
[0006] For a see-through display, a user sees the real world
environment around the user, plus the added image of the scanning
beam display device projected onto the retina. When the user looks
at an object in the field of view, the eye performs three basic
functions. For one function, each eye moves so that the object
appears at the center of vision. For a second function, each eye
adjusts for the amount of light coming into the eye by changing the
diameter of the iris opening. For a third function, each eye
focuses by changing the curvature of the eye lens. If the focal
distance from the third function does not match the distance to the
point of convergence, then the brain detects a conflict. Nausea may
occur.
SUMMARY OF THE INVENTION
[0007] According to the invention, a more lifelike image is
generated with a virtual retinal display by including a method and
apparatus of variable accommodation.
[0008] According to one aspect of the invention, the scanning beam
display device controls the curvature of scanning light waves
impinging on the eye to simulate image points of differing depth.
Images at far distances out to infinity have flat light waves
impinging the eye. Images at near distances have convex-shaped
light waves impinging the eye. Thus, to simulate an object at a far
distance the light waves transmitted from the display to the eye
are flat. To simulate closer objects, the light wave curvature
increases. The eye responds to the changing curvature of the light
waves by altering its focus. The curvature of the generated light
waves relates to a desired, `apparent distance` between a virtual
object and the eye.
[0009] According to another aspect of the invention, a variable
focus lens is included in the virtual retinal display to alter the
shape of the light waves. The lens varies its focal length over
time as desired. For example, for an image that is 640 by 480
pixels, there are 307,200 image elements. The variable focus lens
is able to adjust its focal length fast enough to define a
different focal length for each image element.
[0010] According to another aspect of the invention the variable
focus lens is formed by a resonant crystalline quartz lens. The
resonant lens changes thickness along its optical axis, thus
varying its focal length. The lens varies in focal length with
respect to time. By varying the time when a light pulse enters the
resonant lens, the focus is varied. A non-resonant lens is used in
another embodiment where its response time is fast enough to focus
for each image element.
[0011] According to another aspect of the invention, a device which
changes its index of refraction over time is used instead of a
variable focus lens. In one embodiment an acousto-optical device
(AOD) or an electro-optical device (EOD) is used. In the AOD,
acoustic energy is launched into an acousto-optic material to
control the index of refraction of the AOD. In one embodiment of an
EOD, a lens is coated with a lithium niobate layer. An electric
field is applied across the lithium niobate material to vary the
index of refraction of the coating. Changing the index of
refraction changes the effective focal length of the lens to vary
the focus distance of the virtual image.
[0012] In another embodiment an optical device changes its index of
refraction based upon the intensity (frequency) of an impinging
infrared beam. The current intensity of the infrared beam in effect
sets the current index of refraction for the device. Varying the
intensity of the infrared beam varies the index of refraction to
vary the effective focal length of the optical device.
[0013] Another embodiment includes a compressible, cylindrical
gradient index lens as a focusing element. A cylindrical
piezoelectric transducer compresses an outer shell of the gradient
index cylinder. Compression of the cylinder shifts the physical
location of the lens material to changes the index of refraction
gradient, thereby changing the focal length. Another embodiment
includes a current driven device that uses free-carrier injection
or depletion to change its index of refraction.
[0014] According to another aspect of the invention, a variable
focus lens serves to correct the curvature of the intermediate
image plane for errors introduced by the scanners or from the
aberration of other optical elements. In an exemplary embodiment, a
aberration map of the system is stored in a look-up table in
memory. The aberration map provides correction data for each image
element. The correction data drives the variable focus element to
adjust the focal depth for each image element.
[0015] According to another aspect of the invention, the light
source is moved to vary the focal length instead of introducing a
variable focus lens to vary the focal length.
[0016] According to another aspect of the invention, the light
source emits light toward a mirror that reflects the light toward a
lens of the display. The mirror is movable about an axis causing
the angle of reflection to vary. A control signal determines the
position of the mirror and thus the angle of reflection. As the
angle of reflection varies, the focal distance of light exiting the
lens varies proportionately.
[0017] According to another aspect of the invention, an augmented
display includes variable accommodation. The scanning beam display
is augmented to include a background image upon which a virtual
image is augmented. An object within the virtual image is scanned
to have an apparent distance within the field of view. Thus, a
virtual object may be placed within a real world background view.
The apparent distance is controlled by controlling the curvature of
the light waves which scan the object pixels onto the viewer's
eye.
[0018] According to another aspect of the invention, distance of a
background image object is measured and used to specify the
apparent distance of a virtual object to be placed in proximity to
such background image object.
[0019] According to another aspect of this invention, the intensity
of a virtual image is controlled relative to measured intensity of
a background image. As a result, the relative contrast between the
virtual image and background image may be the same even within
different background image intensities. Further, the virtual image
intensity can be controlled to be approximately the same as the
background image for a more realistic viewing effect.
[0020] One advantage of varying the curvature of light is that the
produced image is more life-like, enhancing the user's feeling of
presence. These and other aspects and advantages of the invention
will be better understood by reference to the following detailed
description taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a block diagram of a virtual retinal display
according to an embodiment of this invention;
[0022] FIG. 2 is an optical schematic of the virtual retinal
display according to an embodiment of this invention;
[0023] FIG. 3 is an optical schematic of the virtual retinal
display according to another embodiment of this invention;
[0024] FIG. 4 is an optical schematic of a virtual retinal display
without a variable focus lens;
[0025] FIG. 5 is an optical schematic of the virtual retinal
display according to another embodiment of this invention;
[0026] FIG. 6 is an optical schematic of the virtual retinal
display according to another embodiment of this invention;
[0027] FIG. 7 is an optical schematic of another virtual retinal
display without a variable focus lens;
[0028] FIG. 8 is a diagram of light directed toward an eye for
depicting light curvature for sequential image elements;
[0029] FIG. 9 is a perspective drawing of an exemplary scanning
subsystem for the display of FIG. 1;
[0030] FIG. 10 is a diagram of a variably transmissive eyepiece for
an embodiment of the display of FIG. 1;
[0031] FIG. 11 is a diagram of an electro-mechanically variable
focus lens for an optics subsystem of FIG. 1 according to an
embodiment of this invention;
[0032] FIG. 12 is a diagram of an alternative variable focus lens
embodiment for the optics subsystem of FIG. 1;
[0033] FIG. 13 is a diagram of another alternative variable focus
lens embodiment for the optics subsystem of FIG. 1;
[0034] FIG. 14 is a diagram of a plurality of cascaded lens for the
optics system of FIG. 1 according to an embodiment of this
invention;
[0035] FIG. 15 is an optical schematic of a virtual retinal display
according to another embodiment of this invention;
[0036] FIG. 16 is an optical schematic of a virtual retinal display
according to another embodiment of this invention;
[0037] FIG. 17 is a diagram of an optical source with position
controller of FIG. 10 and 11 according to an embodiment of this
invention;
[0038] FIG. 18 is a diagram of an optical source with position
controller of FIG. 10 and 11 according to another embodiment of
this invention;
[0039] FIG. 19 is an optical schematic of a virtual retinal display
according to another embodiment of this invention;
[0040] FIG. 20 is a diagram of a display apparatus embodiment of
this invention mounted to eyeglasses that serve as an eyepiece for
the display apparatus;
[0041] FIG. 21 is a diagram of a scanning beam augmented display
embodiment of this invention; and
[0042] FIG. 22 is a diagram of a control portion of the display of
FIG. 21.
DESCRIPTION OF SPECIFIC EMBODIMENTS
Overview
[0043] FIG. 1 is a block diagram of a scanning light beam display
10 having variable accommodation according to an embodiment of this
invention. The display 10 generates and manipulates light to create
color or monochrome images having narrow to panoramic fields of
view and low to high resolutions. Light modulated with video
information is scanned directly onto the retina of a viewer's eye E
to produce the perception of an erect virtual image. The display 10
is small in size and suitable for hand-held operation or for
mounting on the viewer's head. The display 10 includes an image
data interface 11 that receives a video or other image signal, such
as an RGB signal, NTSC signal, VGA signal or other formatted color
or monochrome video or image data signal. Such signal is received
from a computer device, video device or other digital or analog
image data source. The image data interface generates signals for
controlling a light source 12. The generated light is altered
according to image data to generate image elements (e.g., image
pixels) which form an image scanned onto the retina of a viewer's
eye E.
[0044] The light source 12 includes one or more point sources of
light. In one embodiment red, green, and blue light sources are
included. The light sources or their output beams are modulated
according to the input image data signal content to produce light
which is input to an optics subsystem 14. Preferably the emitted
light is spatially coherent.
[0045] The scanning display 10 also includes an optics subsystem
14, a scanning subsystem 16, and an eyepiece 20. Emitted light
passes through the optics subsystem 14 and is deflected by the
scanning subsystem 16. Typically light is deflected along a raster
pattern, although in an alternative embodiment another display
format such as vector imaging can be used. In one embodiment the
scanning subsystem 16 receives a horizontal deflection signal and a
vertical deflection signal derived from the image data interface
11. In another embodiment, the scanning subsystem 16 includes a
mechanical resonator for deflecting passing light.
[0046] According to an aspect of this invention the optics
subsystem 14 includes a device for varying the curvature of light
impinging upon the eye E. According to an alternative aspect of the
invention, the display 10 instead includes a device for moving the
light source position with time to vary the curvature of light
impinging upon the eye E.
Embodiments in which Optics Subsystem Varies Curvature
[0047] FIGS. 2-5 show optical schematics for alternative
embodiments in which the optics subsystem 14 includes a variable
focus lens 22 for varying the curvature of light impinging upon the
eye E. FIGS. 2 and 3 are similar but have the variable focus lens
22 for varying curvature located at different locations. In the
FIG. 2 embodiment light from point source(s) 12 passes through the
variable focus lens 22 then through a collimating lens 24 before
travelling to the scanning subsystem 16 and eyepiece 20. In the
FIG. 3 embodiment light from the point source(s) 12 passes through
a collimating lens 24 then through the variable focus lens 22
before travelling to the scanning subsystem 16 and eyepiece 20. The
light passing from the eyepiece 20 to the eye E has its curvature
varied over time based upon the control of variable focus lens 22.
For some image elements the curvature is of one contour to cause
the eye to focus at a first focal length. For other image elements
the curvature is of another contour to causes the eye to focus at a
second focal length. By controlling the curvature, the display 10
controls the apparent focus of the eye, and thus causes different
image elements to appear to be located at different distances.
[0048] FIG. 4 shows an optical schematic of a display without the
variable focus lens 22. Note that the light impinging on the eye E
is formed by planar waves. In such embodiment all optical elements
appear at a common, indeterminate depth.
[0049] FIGS. 5 and 6 are similar to FIGS. 2 and 3, but are for an
optics subsystem 14 which converges the light rather than one which
collimates the light. FIG. 7 shows an optical schematic of a
virtual retinal display without the variable focus lens 22. Note
that the light impinging on the eye E for the FIG. 7 embodiment is
formed by planar waves. In such embodiment all optical elements
appear at a common indeterminate depth. In FIG. 5 light from a
point source(s) 12 passes through the variable focus lens 22 then
through a converging lens 24 before travelling to the scanning
subsystem 16 and eyepiece 20. In the FIG. 6 embodiment light from
the point source(s) 12 passes through a converging lens 26 then
through the variable focus lens 22 before travelling to the
scanning subsystem 16 and eyepiece 20. The light passing from the
eyepiece 20 to the eye E has its curvature varied over time based
upon the control of variable focus lens 22.
[0050] FIG. 8 shows a pattern of light impinging on the eye. The
scanning beam display device controls the curvature of scanning
light waves impinging on the eye to simulate image points of
differing depth. Images at far distances out to infinity have flat
light waves impinging the eye. Images at near distances have
convex-shaped light waves impinging the eye. The light is shown as
a sequence of light. For a first image element 26 the corresponding
light 28 has one curvature. For another image element 30, the
corresponding light 32 has another curvature. Light 36, 40, 44 for
other image elements 34, 38, 40 also is shown. A sequence of image
elements is scanned upon the eye E to generate an image perceived
by the eye. To simulate an object at a far distance the light waves
transmitted from the display to the eye are flat. To simulate
closer objects, the light wave curvature increases. The curvature
of the generated light waves relates to the desired, `apparent
distance` (i.e., focus distance) between a virtual object and the
eye. The eye responds to the changing curvature of the light waves
by altering its focus. The curvature of the light changes over time
to control the apparent depth of the image elements being
displayed. Thus, varying image depth is perceived for differing
portions of the scanned image.
Light Source
[0051] The light source 12 includes a single or multiple light
sources. For generating a monochrome image a single monochrome
source typically is used. For color imaging, multiple light sources
are used. Exemplary light sources are colored lasers, laser diodes
or light emitting diodes (LEDs). Although LEDs typically do not
output coherent light, lenses are used in one embodiment to shrink
the apparent size of the LED light source and achieve flatter wave
fronts. In a preferred LED embodiment a single mode, monofilament
optical fiber receives the LED output to define a point source
which outputs light approximating coherent light.
[0052] In one embodiment red, green, and blue light sources are
included. In one embodiment the light source 12 is directly
modulated. That is, the light source 12 emits light with an
intensity corresponding to image data within the image signal
received from the image data interface 11. In another embodiment
the light source 12 outputs light with a substantially constant
intensity that is modulated by a separate modulator in response to
the image datadrive signal. The light output along an optical path
thus is modulated according to image data within the image signal
received from the image data interface 11. Such modulation defines
image elements or image pixels. Preferably the emitted light 31 is
spatially coherent.
[0053] Additional detail on these and other light source 12
embodiments are found in U.S. Pat. No. 5,596,339 to Furness, et
al., entitled "Virtual Retinal Display with Fiber Optic Point
Source" which is incorporated herein by reference.
Image Data Interface
[0054] As described above, the image data interface 11 receives
image data to be displayed as an image data signal. In various
embodiments, the image data signal is a video or other image
signal, such as an RGB signal, NTSC signal, VGA signal or other
formatted color or monochrome video or graphics signal. An
exemplary embodiment of the image data interface 11 extracts color
component signals and synchronization signals from the received
image data signal. In an embodiment in which an image data signal
has embedded red, green and blue components, the red signal is
extracted and routed to a modulator for modulating a red light
point source output. Similarly, the green signal is extracted and
routed to a modulator for modulating the green light point source
output. Also, the blue signal is extracted and routed to a
modulator for modulating the blue light point source output.
[0055] The image data signal interface 11 also extracts a
horizontal synchronization component and vertical synchronization
component from the image data signal. In one embodiment, such
signals define respective frequencies for horizontal scanner and
vertical scanner drive signals routed to the scanning subsystem
16.
Scanning Subsystem
[0056] The scanning subsystem 16 is located after the light sources
12, either before or after the optics subsystem 14. In one
embodiment, the scanning subsystem 16 includes a resonant scanner
200 for performing horizontal beam deflection and a galvanometer
for performing vertical beam deflection. The scanner 200 serving as
the horizontal scanner receives a drive signal having a frequency
defined by the horizontal synchronization signal extracted at the
image data interface 11. Similarly, the galvanometer serving as the
vertical scanner receives a drive signal having a frequency defined
by the vertical synchronization signal VSYNC extracted at the image
data interface. Preferably, the horizontal scanner 200 has a
resonant frequency corresponding to the horizontal scanning
frequency.
[0057] Referring to FIG. 9, one embodiment of the scanner 200
includes a mirror 212 driven by a magnetic circuit so as to
oscillate at a high frequency about an axis of rotation 214. In
this embodiment the only moving parts are the mirror 212 and a
spring plate 216. The optical scanner 200 also includes a base
plate 217 and a pair of electromagnetic coils 222, 224 with a pair
of stator posts 218, 220. Stator coils 222 and 224 are wound in
opposite directions about the respective stator posts 218 and 220.
The electrical coil windings 222 and 224 may be connected in series
or in parallel to a drive circuit as discussed below. Mounted on
opposite ends of the base plate 217 are first and second magnets
226, the magnets 226 being equidistant from the stators 218 and
220. The base 217 is formed with a back stop 232 extending up from
each end to form respective seats for the magnets 226.
[0058] The spring plate 216 is formed of spring steel and is a
torsional type of spring having a spring constant determined by its
length and width. Respective ends of the spring plate 216 rest on a
pole of the respective magnets 226. The magnets 226 are oriented
such that they have like poles adjacent the spring plate.
[0059] The mirror 212 is mounted directly over the stator posts 218
and 220 such that the axis of rotation 214 of the mirror is
equidistant from the stator posts 218 and 220. The mirror 212 is
mounted on or coated on a portion of the spring plate.
[0060] Magnetic circuits are formed in the optical scanner 200 so
as to oscillate the mirror 212 about the axis of rotation 214 in
response to an alternating drive signal. One magnetic circuit
extends from the top pole of the magnets 226 to the spring plate
end 242, through the spring plate 216, across a gap to the stator
218 and through the base 217 back to the magnet 226 through its
bottom pole. Another magnetic circuit extends from the top pole of
the other magnet 226 to the other spring plate end, through the
spring plate 216, across a gap to the stator 218 and through the
base 217 back to the magnet 226 through its bottom pole. Similarly,
magnet circuits are set up through the stator 220.
[0061] When a periodic drive signal such as a square wave is
applied to the oppositely wound coils 222 and 224, magnetic fields
are created which cause the mirror 212 to oscillate back and forth
about the axis of rotation 214. More particularly, when the square
wave is high for example, the magnetic field set up by the magnetic
circuits through the stator 218 and magnets 226 and 228 cause an
end of the mirror to be attracted to the stator 218. At the same
time, the magnetic field created by the magnetic circuits extending
through the stator 220 and the magnets 226 cause the opposite end
of the mirror 212 to be repulsed by the stator 220. Thus, the
mirror is caused to rotate about the axis of rotation 214 in one
direction. When the square wave goes low, the magnetic field
created by the stator 218 repulses the end of the spring plate 216.
At the same time, the stator 220 attracts the other end of the
spring plate 216. Both forces cause the mirror 212 to rotate about
the axis 214 in the opposite direction.
[0062] In alternative embodiments, the scanning subsystem 14
instead includes acousto-optical deflectors, electro-optical
deflectors, rotating polygons or galvanometers to perform the
horizontal and vertical light deflection. In some embodiments, two
of the same type of scanning device are used. In other embodiments
different types of scanning devices are used for the horizontal
scanner and the vertical scanner.
Eyepiece
[0063] Referring to FIGS. 2-4 the eyepiece 20 typically is a
multi-element lens or lens system receiving the light beam(s) prior
to entering the eye E. In alternative embodiments the eyepiece 20
is a single lens (see FIGS. 5-7). The eyepiece 20 serves to relay
the rays from the light beam(s) toward a viewer's eye. In
particular the eyepiece 20 contributes to the location where an
exit pupil of the scanning display 10 forms. The eyepiece 20
defines an exit pupil at a known distance d from the eyepiece 20.
Such location is the approximate expected location for a viewer's
eye E.
[0064] In one embodiment the eyepiece 20 is an occluding element
which does not transmit light from outside the display device 10.
In an alternative embodiment, an eyepiece lens system 20 is
transmissive to allow a viewer to view the real world in addition
to the virtual image. In yet another embodiment, the eyepiece is
variably transmissive to maintain contrast between the real world
ambient lighting and the virtual image lighting. Referring to FIG.
10, a photosensor 300 detects an ambient light level. Responsive to
the detected light level, a control circuit 302 varies a bias
voltage across a photochromatic material 304 to change the
transmissiveness of the eyepiece 20. Where the ambient light level
is undesirably high, the photochromatic material 304 blocks a
portion of the light from the external environment so that the
virtual image is more readily perceivable.
Optics Subsystem
[0065] Returning to FIGS. 2-7, the optics subsystem 14 receives the
light output from the light source, either directly or after
passing through the scanning subsystem 16. In some embodiments the
optical subsystem collimates the light. In another embodiment the
optics subsystem converges the light. Left undisturbed the light
converges to a focal point then diverges beyond such point. As the
converging light is deflected, however, the focal point is
deflected. The pattern of deflection defines a pattern of focal
points. Such pattern is referred to as an intermediate image
plane.
[0066] According to an aspect of the invention, the optics
subsystem 14 includes an optical device for varying the curvature
of light over time. Specifically the curvature pattern of the light
entering the eye E for any given image element is controlled via
the variable focus lens 22. In some embodiments the lens 22 has its
focus varied by controlling the thickness of the lens 22. In other
embodiment the lens 22 has its focus varied by varying the index of
refraction of the lens 22.
[0067] The curvature of the light exiting lens 22 is controlled by
changing the shape of the lens 22 or by changing the index of
refraction of the lens 22. A lens which changes its shape is shown
in FIG. 11 and will be referred to as an electro-mechanically
variable focus lens (VFL) 320. A central portion 322 of the VFL 320
is constructed of a piezoelectric resonant crystalline quartz. In
operation, a pair of transparent conductive electrodes 324 provide
an electrical field that deforms the piezoelectric material in a
known manner. Such deformation changes the thickness of the central
portion 322 along its optical axis to effectively change the focus
of the VFL 320.
[0068] Because the VFL 320 is a resonant device, its focal length
varies periodically in a very predictable pattern. By controlling
the time when a light pulse enters the resonant lens, the effective
focal position of the VFL 320 can be controlled.
[0069] In some applications, it may be undesirable to selectively
delay pulses of light according to the resonant frequency of the
VFL 320. In such cases, the VFL 320 is designed to be nonresonant
at the frequencies of interest, yet fast enough to focus for each
image element.
[0070] In another alternative embodiment, the variable focus lens
is formed from a material that changes its index of refraction in
response to an electric field or other input. For example, the lens
material may be an electrooptic or acoustooptic material. In the
preferred embodiment, the central portion 322 (see FIG. 10) is
formed from lithium niobate, which is both electrooptic and
acoustooptic. The central portion 322 thus exhibits an index of
refraction that depends upon an applied electric field or acoustic
energy. In operation, the electrodes 324 apply an electric field to
control the index of refraction of the lithium niobate central
portion 322. In another embodiment a quartz lens includes a
transparent indium tin oxide coating.
[0071] In another embodiment shown in FIG. 12, a lens 330 includes
a compressible cylindrical center 332 having a gradient index of
refraction as a function of its radius. A cylindrical piezoelectric
transducer 334 forms an outer shell that surrounds the cylindrical
center 332. When an electric filed is applied to the transducer
334, the transducer 334 compresses the center 332. This compression
deforms the center 332, thereby changing the gradient of the index
of refraction. The changed gradient index changes the focal length
of the center 332.
[0072] In another embodiment shown in FIG. 13 the variable focus
element is a semiconductor device 350 that has an index of
refraction that depends upon the free carrier concentration in a
transmissive region 352. Applying either a forward or reverse
voltage to the device 350 through a pair of electrodes 354 produces
either a current that increases the free-carrier concentration or a
reverse bias that depletes the free carrier concentration. Since
the index of refraction depends upon the free carrier
concentration, the applied voltage can control the index of
refraction.
[0073] In still another embodiment shown in FIG. 14 a plurality of
lenses 360-362 are cascaded in series. One or more piezoelectric
positioners 364-366 move one or more of the respective lenses
360-362 along the light path changing the focal distance of the
light beam. By changing the relative position of the lenses to each
other the curvature of the light varies.
[0074] One use of the variable focus lens 22 is to correct the
curvature of an intermediate image plane for errors introduced by
the scanning system 16 or for aberrations introduced by other
optical elements. For example, in the embodiment of FIG. 13 a
aberration map of the overall optical path is stored in a look-up
table in memory 370. The aberration map is a set of determined
correction data representing the desired amount or variation in the
focal length of the variable focus element for each pixel of an
image. Control electronics 372 retrieve a value from the table for
each pixel and apply a corresponding voltage or other input to
adjust the focal depth to correct for the aberration.
Light Source That Moves to Vary Light Wave Curvature
[0075] FIGS. 15 and 16 show embodiments of a scanning display
50/50' in which the light source 13 includes one or more moving
point sources 15. FIG. 15 shows a display device 50 having an
optics subsystem 14 and eyepiece 20 that collimates the light. FIG.
16 shows a display device 50' having an optics subsystem 14 and
eyepiece 20 that converges the light. In each of the embodiments of
FIGS. 15 and 16, the point sources 15 move along an axis 54 normal
to a plane of the optics subsystem 14. Thus, the point sources 15
are moved either closer to or farther from the optics 14. The
changing distance between the point source 15 and the optics 14
changes the apparent distance of the point source 15 as viewed
through the lens 14. Moving the point source in one direction
causes a virtual image portion to appear farther away to the
viewer. Moving the point source 15 in the opposite direction causes
the virtual image portion to appear closer to the viewer. This is
represented by the varying curvature of the light wavefronts 56
shown in FIGS. 15 and 16. By controlling the distance of the point
source 15 from the optics 14 the focus of an image portion
varies.
[0076] Responsive to a control signal, a position controller 60
determines the distance from the point source 15 to the optics 14
for each pixel or group of pixels. In one embodiment, the
controller 60 includes a piezoelectric actuator that moves the
point sources 15. In another embodiment the controller 60 includes
an electromagnetic drive circuit that moves the point sources 15.
The axis of motion of actuator or drive circuit is aligned with the
direction at which the point sources 15 emit light, so that motion
of the point sources 15 does not produce shifting of the location
of the respective pixel in the user's field of view.
[0077] FIG. 17 shows an embodiment for moving the apparent location
of the point source 15. Light emitted from a light source 12
impinges on a partially reflective surface 122 that deflects the
light toward a mirror 124. The mirror 124 reflects the light back
through the partially reflective surface 122, which transmits the
light to the optics 14. The angle at which the light impinges the
optics 14 is determined by the orientation of the mirror 124. Such
orientation is adjustable. In one embodiment the mirror 124 is
movable about a pivot line 126. In an initial position the mirror
124 orientation is normal to the light impinging its surface. For a
movement of the mirror 124 by an angle .delta.z the focal point of
the light exiting the optics 14 varies by a distance .DELTA.z and a
height .DELTA.h. For a mirror 124 which receives the light at a
distance w much greater than the arc distance .delta.z, the
distance .DELTA.z is much greater than the change in height
.DELTA.h. Accordingly, the height .DELTA.h differential is not
significant for many applications. Rotation of the mirror 124 thus
varies the focal distance for each image pixel without
significantly affecting the apparent location of the pixel.
[0078] FIG. 18 shows a light source 13' according to another
embodiment of this invention. The light source includes a light
emitter 15 that emits a beam of light. In one embodiment the light
emitter 15 is a laser diode. In another embodiment, the light
emitter 15 is a light emitting diode with optics for making the
output light coherent.
[0079] The light emitter 15 is carried by a support 64. In one
embodiment the support 64 is formed of spring steel and is a
cantilever type of spring. The cantilever spring has a spring
constant determined by its length, width and thickness. Preferably,
the support 64 is resonant with a high Q value such that once the
support starts moving very little energy is lost. As a result, very
little energy is added during each period of movement to maintain a
constant amplitude of motion of the support 64. For a high Q system
the energy loss per cycle is less than 0.001%. The support 64 is
anchored at one end 65 and is free at an opposite end 67.
Preferably, a position sensor monitors the position of the support
64 and light emitter 15. In some embodiments a common mode
rejection piezoelectric sensor 68 is used. In other embodiments a
sensor 70 responsive to changing inertia is used. An exemplary
sensor 68 is described in such U.S. Pat. No. 5,694,237 issued Dec.
2, 1997 entitled "Position Detection of Mechanical Resonant Scanner
Mirror."The light source 13' also includes a base 76, a cap 78 and
an electromagnetic drive circuit 60, formed by a permanent magnet
82 and an electromagnetic coil 84. The anchored end 65 of the
support 64 is held to the permanent magnet 82 by the cap 78. The
permanent magnet 82 is mounted to the base 76. The electromagnetic
coil 84 receives the control signal causing a magnetic field to act
upon the support 64. In another embodiment a piezoelectric actuator
is used instead of an electromagnetic drive circuit. The drive
circuit 60 moves the support 64 and light emitter 15 along an axis
88 way from or toward the optics 14 (of FIG. 15 or 16) to vary the
focal distance of the light exiting the display.
[0080] In some embodiments the controller 60 moves the light
emitter 15 to generate a flat post-objective scan field. In effect
the controller varies the focal point of the emitted light to occur
in a flat post-objective image plane for each pixel component of an
intermediary image plane 18 (see FIG. 19). FIG. 19 shows a point
source 15 at three positions over time, along with three
corresponding focal points F1, F2 and F3 along an intermediary
image plane 18.
[0081] In another embodiment the curvature of the intermediary real
image is varied to match the curvature of an eyepiece 20' as shown
in FIG. 20. As the position of the light emitter 15 varies, the
curvature of the image light 110 varies. As the light is scanned
along the eyepiece 20', the curvature of the light is varied to
match the curvature of the eyepiece 20' at the region where the
light impinges the eyepiece 20'. FIG. 20 shows a first curvature
112 for one position of the light emitter 15 and a second curvature
114 for another position of the light emitter 15.
Augmented Scanning Beam Display
[0082] FIG. 21 shows a preferred embodiment in which the scanning
beam display is an augmented display 150 which generates a virtual
image upon a background image. The background image may be an
ambient environment image or a generated image. The virtual image
is overlaid upon all or a portion of the background image. The
virtual image may be formed of virtual two-dimensional or
three-dimensional objects which are to be placed with a perceived
two-dimensional or three-dimensional background image environment.
More specifically, virtual objects are displayed to be located at
an apparent distance within the field of view.
[0083] As previously described, the display device controls the
curvature of scanning light waves impinging on the eye to simulate
image points of differing depth. Images at far distances out to
infinity have flat light waves impinging the eye. Images at near
distances have convex-shaped light waves impinging the eye. To
simulate an object at a far distance the light waves transmitted
from the display to the eye are flat. To simulate closer objects,
the light wave curvature increases. The eye responds to the
changing curvature of the light waves by altering its focus. The
curvature of the generated light waves relates to a desired
apparent focal distance between a virtual object and the eye.
[0084] The augmented scanning beam display 150 receives an image
signal 152 from an image source 154. The display 150 includes an
image data interface 11, one or more light sources 12, a lensing or
optics subsystem 14, a scanning subsystem 16, a beamsplitter 156, a
concave mirror 158 and an eyepiece 20. Like parts performing the
same or similar functions relative to the display 10 of FIG. 1 are
given the same part numbers. In one embodiment, the beamsplitter
156 and mirror 158 serve as the eyepiece. In other embodiments
another lens (not shown) is included to serve as eyepiece 20.
[0085] The image source 154 which generates the image signal 152 is
a computer device, video device or other digital or analog image
data source. The image signal 152 is an RGB signal, NTSC signal,
VGA signal, SVGA signal, or other formatted color or monochrome
video or image data signal. In response to the image signal 152,
the image data interface 11 generates an image content signal 160
for controlling the light source 12 and one or more synchronization
signals 162 for controlling the scanning subsystem 16.
[0086] The light source 12 includes one or more point sources of
light. In one embodiment red, green, and blue light sources are
included. In one embodiment the light source 12 is directly
modulated. That is, the light source 12 emits light with an
intensity corresponding to the image content signal 160. In another
embodiment the light source 12 outputs light with a substantially
constant intensity that is modulated by a separate modulator in
response to the signal 160. Light 164 is output from the light
source 12 along an optical path, being modulated according to the
image data within the image content signal 160. Such modulation
defines image elements or image pixels. Preferably the emitted
light 164 is spatially coherent.
[0087] The light 164 is output to the optics subsystem 14 and the
scanning subsystem 16. The scanning subsystem 16 includes a
horizontal scanner and a vertical scanner. In one embodiment, the
horizontal scanner includes a mechanical resonator for deflecting
passing light. Typically the light is deflected along a raster
pattern, although in an alternative embodiment another display
format such as vector imaging can be used.
[0088] The scanning subsystem 16 deflects the light along a raster
pattern toward the eye E, or as in the embodiment illustrated,
toward the beamsplitter 156. The beamsplitter 156 passes both
background light 166 and virtual image light 168 to the viewer's
eye E. The concave mirror 158 focuses the light onto the eye E. The
eye perceives the background image and an overlaid virtual image.
The image pixels forming the virtual image are scanned onto the
viewer's eye. When the virtual image is updated and rescanned
periodically at a requisite frequency, the viewer perceives a
continuous, virtual image.
[0089] The augmented display 150 also includes one or more light
sensors 170, 172 and a controller 174. Referring to FIGS. 21 and
22, light sensor 170 detects the intensity of the background light
166. The controller 174 receives the detected light intensity and
generates a signal 176 which in response adjusts the intensity of
the virtual image light 168. In one embodiment the virtual image
light 168 intensity is adjusted by controlling the intensity of
light 164 output by the light source 12. For example, controller
174 outputs a control signal 176 to the light source 12 to vary the
light source 12 intensity.
[0090] Sensor 172 detects the distance of a background object or
other focal viewing point of the background image light 166. Such
sensor 172 is a conventional sensor of the kind used in cameras for
determining object distance in connection with a camera's autofocus
function. The controller 174 with the sensor 172 generates a signal
178 for controlling the apparent distance of a virtual object to be
overlaid upon the background object. In one embodiment the control
signal 178 is input to the variable focus lens 22 to adjust the
curvature of the light waves forming the virtual image light 168.
In an alternative embodiment, the control signal 178 moves the
light source 12 to vary the curvature of the light waves forming
the virtual image light 168. In some embodiments, multiple sensors
172 are included for measuring background distance for many points
within the background viewing field. The measuring points
correspond to differing areas within the field of view. The
measured distance for a given area is used to specify a distance
for a virtual object to be overlaid upon the corresponding image
area. Although, the term overlaid is used, the virtual object may
be in part overlaid and in part underlaid relative to a background
object or background image area, as desired. Accordingly, a virtual
image area is generated having an apparent distance which is
correlated to a real world image, and more particularly, to a real
world image distance. More generally, a virtual image area is
generated having an apparent distance which is correlated to a
background image, and more particularly, to a background image
distance.
[0091] For varying applications, in addition to controlling the
content and positioning of a virtual object, the object's shading,
shadowing and other imaging effects can be controlled to achieve a
desired realistic, surrealistic, or non-realistic effect. For
example, in a gaming application virtual scenes may be superimposed
upon a player's immediate background environment (e.g., the
player's home, the woods, et cet.). In a flight simulator,
simulated terrain may be the source of the background image light,
while simulated aircraft, targets or other objects may serves as
the virtual objects. In such example, the terrain simulator
replaces or provides the inputs to the sensors 170, 172.
[0092] In some embodiments, the background area onto which an
opaque virtual object is overlaid is blanked. Commonly-assigned
U.S. patent application Ser. No. 09/009,759 of Charles D. Melville
entitled, Augmented Imaging Using A Silhouette To Improve Contrast,
filed Jan. 20, 1998 is incorporated herein by reference and made a
part hereof. Such application describes the use of a silhouette
display to blank out areas of background light to improve the
contrast for a virtual image area.
[0093] Although preferred embodiments of the invention have been
illustrated and described, various alternatives, modifications and
equivalents may be used. Therefore, the foregoing description
should not be taken as limiting the scope of the inventions which
are defined by the appended claims.
* * * * *